import java.math.*;

public class BigIntegerDemo {
    public static void main(String[] args) {

        // create 3 BigInteger objects
        BigInteger bi1, bi2, bi3;

        // create a BigInteger exponent
        BigInteger exponent = new BigInteger("2");

        bi1 = new BigInteger("7");
        bi2 = new BigInteger("20");

        // perform modPow operation on bi1 using bi2 and exp
        //7^2除以20的余数就是bi3
        bi3 = bi1.modPow(exponent, bi2);

        String str = bi1 + "^" + exponent + " mod " + bi2 + " is " + bi3;

        // print bi3 value
        System.out.println(str);
    }
}